Process for Preparing Dynamically Vulcanized Alloys

ABSTRACT

This invention relates to the preparation of a dynamically vulcanized alloy comprising at least one elastomer and at least one thermoplastic resin, having a G′ at 1% strain and 100° C. as determined according to ASTM D7605 of about 4,500 to about 7,500 kPa. More specifically, the process produces dynamically vulcanized alloys with unique morphological features which have good impermeability and low temperature flexibility. In the process, the thermoplastic resin is added into the extruder in two stages with an intermediate addition of a compatibilizer. Also during the final addition of thermoplastic resin, the elastomeric curatives are added to the extruder.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of pending InternationalApplication No. PCT/US2013/065001, filed on Oct. 15, 2013, claimingpriority to U.S. patent application Ser. No. 61/740114, filed on Dec.20, 2012, the disclosures of which are fully incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to processes for preparingdynamically vulcanized alloys, of elastomer and thermoplastic resins,having certain elastic shear and stiffness modulus values.

BACKGROUND OF THE INVENTION

Various types of thermoplastic elastomer compositions containingelastomers, both cured and uncured, and thermoplastic resins, are knownin the industry as either thermoplastic plastic vulcanizates (TPVs) oras dynamically vulcanized alloys (DVAs). The elastomer is dispersed inthe thermoplastic resin, providing flexibility to the material due tothe elastomer and reprocessability due to the thermoplastic resin. Thesematerials are known to be useful in a variety of applications includingautomotive parts, such as bumpers, knobs, and trim, electrical andapplications, such as cable jacketing and connectors, and industrialapplications, such as piping, o-rings, sleeves, extruded spiral hoses,and weather stripping. For all of these known applications, the TPVs orDVAs are cast or molded to form the final products.

The conventional fabrication process is a multiple-step process havingthe following steps. The compound is produced by (i) preparing a rubbermaster batch by mixing, at temperatures below the cross-linkingtemperature, the elastomer and curative until a uniform mix state isobtained (this is often referred to as pre-conditioning) and (ii)premixing a resin master batch comprising a thermoplastic resin andplasticizers. If desired, fillers such as carbon, oil, calciumcarbonate, nanofillers, etc., may also be added to the rubber masterbatch. A thermoplastic resin masterbatch is mixed typically in a twinscrew extruder by mixing the resin and plasticizers. The resinmasterbatch may then be pelletized. The rubber master batch, resinmaster batch, and all remaining components are then fed into a mixer, aswell as any desired secondary components, and mixed under shearconditions. The elastomer component is vulcanized during the meltmixing.

Commercial TPVs are typically not compounded or prepared for use inlow-permeability applications, and are generally polyolefin basedcompounds. The processes existing to produce the polyolefin based TPVare operated at high extruder screw speeds (>greater than 250revolutions/minute) and corresponding high peak shear rates. The higherscrew speeds allows for high net output. See U.S. Pat. No. 5,298,211 andU.S. Pat. No. 4,594,390. The processes utilize the high shear rates toreduce rubber particle size, simultaneously during the curing reactionin the extruder. The typical rubber particle size for such thermoplasticelastomers is above 1 micron size, often 3 to 10 microns. An energyefficient process for producing sub-micron size particles is differentfrom the above noted patents due to the fact that the basic rubberparticle structure is thought to be formed in part due to an interfacialreaction between the rubber and the thermoplastic prior to cure.

DVAs compounded for low permeability [or stated alternatively: highimpermeability] applications comprise low-permeability thermoplasticresin, such as polyamide or a blend of polyamides, in which there isdispersed a low-permeability rubber. Such low permeability rubbersinclude butyl rubber, halobutyl rubbers, or brominated isobutylenepara-methylstyrene copolymers. The rubber is cured under conditions ofdynamic vulcanization (curing the rubber during melt mixing as opposedto static curing that typically occurs in a rubber mold) and isintimately and uniformly dispersed as a particulate phase within acontinuous phase of the thermoplastic resin. For low permeabilityapplications, it is desired to achieve a composition having sub-micronsize dispersed rubber particles. This dispersed particle size assiststhe material in having elastic properties.

The elastic nature is desirable for applications requiring flexibility,strength, and elongation. Such properties are also desirable in tirematerials. Thus, in recent years, the use of DVAs as tire inner linerlayers has been explored. The thermoplastic resin provides a very lowpermeability to the inner liner layer while the elastomer providesflexibility and durability to the inner liner layer. As thethermoplastic resin provides a very low permeability, in comparison toan all elastomeric inner liner composition, the inner liner layer formedfrom DVA can be formed as a very thin layer. Conventional inner linerlayers, comprised of only a base elastomer(s), typically have athickness or gauge in the range of 1.25 to 7.0 mm while inner linerlayers formed from DVA have typically a thickness range of 0.25 mm to0.08 mm.

However, the past work of Applicants and others in using DVA for tireinnerliners has highlighted the need for continued improvement in theprocess of preparing DVAs. As noted above, TPVs and DVAs haveconventionally been molded or cast to form the end products. Filmshaving a thickness in range of 0.25 mm to 0.08 mm are not molded orcast, but must be extruded or blown thru a suitable die. The morphologyof the DVA material, which is impacted by the DVA manufacturing process,has a significant impact on the ability to obtain a quality extrusionand quality film. In particular, a DVA film's low temperature durabilityis dependent not only on the composition but also on the morphology ofthe final product.

SUMMARY OF THE INVENTION

The present invention is directed to a process for preparing adynamically vulcanized alloy (“DVA”), comprising a thermoplastic resinand an elastomer, having a G′ at 1% strain and 100° C. as determinedaccording to ASTM D7605 of about 4,500 to about 7,500 kPa. Preferablythe elastomer is a low-permeability rubber. In the process, theelastomer and the thermoplastic resin are fed into a mixer where themixture is dynamically vulcanized. The thermoplastic resin can be addedinto the extruder in two stages with an intermediate addition of acompatibilizer or other components. Elastomeric curatives are added tothe extruder in a manner that permits the decoupling of the rubber andresin grafting and the rubber vulcanization. Thus, some or all of thecurative may be added at the initial feed throat if the curative has adelayed cure time, i.e. a long induction time; or the curative is addeddownstream from the initial feed throat introduction of the rubber intothe extruder; this addition may occur in conjunction with athermoplastic resin addition, in-between thermoplastic resin additions,or after all thermoplastic resin has been added. The process producesdynamically vulcanized alloys with unique morphological features whichhave good impermeability and low temperature flexibility.

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription and appended claims.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 is a schematic illustration of an extruder for manufacturingdynamically vulcanized alloys in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Various specific embodiments, versions, and examples are describedherein, including exemplary embodiments and definitions that are adoptedfor purposes of understanding the claimed invention. While the followingdetailed description gives specific preferred embodiments, those skilledin the art will appreciate that these embodiments are exemplary only,and that the invention can be practiced in other ways. For purposes ofdetermining infringement, the scope of the invention will refer to anyone or more of the appended claims, including their equivalents, andelements or limitations that are equivalent to those that are recited.Any reference to the “invention” may refer to one or more, but notnecessarily all, of the inventions defined by the claims.

Polymer may be used to refer to homopolymers, copolymers, interpolymers,terpolymers, etc. Likewise, a copolymer may refer to a polymercomprising at least two monomers, optionally with other monomers. When apolymer is referred to as comprising a monomer, the monomer is presentin the polymer in the polymerized form of the monomer or in thepolymerized form of a derivative from the monomer (i.e., a monomericunit). However, for ease of reference the phrase comprising the(respective) monomer or the like is used as shorthand.

Elastomer refers to any polymer or composition of polymers consistentwith the ASTM D1566 definition: “a material that is capable ofrecovering from large deformations, and can be, or already is, modifiedto a state in which it is essentially insoluble, if vulcanized, (but canswell) in a solvent.” In the present invention, elastomers may bereferred to as polymers, elastomeric polymers, or rubbers; the termelastomer may be used herein interchangeably with the term rubber orpolymer.

The term “phr” is parts per hundred rubber or “parts”, and is a measurecommon in the art wherein components of a composition are measuredrelative to a total of all of the elastomer components. The total phr orparts for all rubber components, whether one, two, three, or moredifferent rubber components is present in a given recipe is normallydefined as 100 phr. All other non-rubber components are ratioed againstthe 100 parts of rubber and are expressed in phr. This way one caneasily compare, for example, the levels of curatives or filler loadings,etc., between different compositions based on the same relativeproportion of rubber without the need to recalculate percentages forevery component after adjusting levels of only one, or more,component(s).

The terms “vulcanized” or “cured” refers to the chemical reaction thatforms bonds or cross-links between the polymer chains of an elastomer.

The term “dynamic vulcanization” is used herein to connote avulcanization process in which a vulcanizable elastomer, present with athermoplastic resin, is vulcanized under conditions of high shear. As aresult of the shear mixing, the vulcanizable elastomer is simultaneouslycrosslinked and dispersed as fine particles of a “micro gel” within thethermoplastic resin, creating a dynamically vulcanized alloy (“DVA”).The unique characteristic of the DVA is that, notwithstanding the factthat the elastomer component may be fully cured, the DVA can beprocessed and reprocessed by conventional rubber processing techniquessuch as extrusion, injection molding, compression molding, etc. Scrap orflashing can be salvaged and reprocessed.

The terms “downstream” and “upstream” when discussing a process or anextruder are given conventional terms in the art. When referencingsomething as ‘downstream’ in the process or extruder, it means a pointin time or location in the process or extruder that is after thereferenced point. When referencing something as ‘upstream’ in theprocess or extruder, it means a point in time or location in the processor extruder that is before the referenced point. For example, if B isintroduced downstream of A, then B is introduced into the process orextruder after A and conversely if B is introduced upstream of A, thenit is introduced before A.

The DVA of the present invention, made by the inventive process, has adesired morphology wherein the elastomer is uniformly dispersed as fineparticles within the thermoplastic resin. The thermoplastic resincomponent forms the continuous phase and the elastomer is the dispersedphase even where the rubber to resin ratio is 1.0 or more. The dispersedparticle size of the elastomer and the structure of the resin phase arecontrolled to improve the durability of the DVA, in particulardurability at low temperatures.

As discussed above, for conventional polyolefin TPV with a large micronsize dispersed particle size, high screw speeds and shear rates areconventional. However, the thermoplastic resins used in low permeabilityapplications require the use of lower screw speeds and relatively lowershear rates. The reason for the lower screw speed operation is the needfor completing several reactions, in sequence along the screw axis tocreate the small rubber particle morphology and completegrafting/compatibilizing or curing reactions.

Applicants have determined that one of the key reactions for generatinga desirable mostly sub-micron morphology is the interfacial reactionbetween the thermoplastic resin and rubber polymer chains. In the lowpermeability materials this interfacial reaction, also known as graftingbetween the thermoplastic resin and the elastomer, needs to occur beforea significant amount reactive sites in the rubber are consumed by therubber curing reaction. For purposes of this invention, a significantamount of reactive sites in the rubber would be equal or greater than30%, or alternatively equal or greater than 40%; thus, significant curehas taken place when more this amount of the reactive sites in therubber have been consumed by cross-linking to other reactive sites withthe assistance of a curing agent. Additionally, to assist indifferentiating between the two reactions that will occur during mixingin accordance with the present invention, for purposes of this inventioninterfacial reaction/grafting shall refer to bonding between elastomersand thermoplastic resins, and curing shall be limited to cross-linkingof the elastomer itself accomplished by the assistance of a separatecuring agent that is not a thermoplastic resin. Therefore, significantcure of rubber should take place after the substantial completion of theinterfacial reaction/grafting, thereby creating the desired submicronelastomeric particles size in a continuous thermoplastic resin matrix,also referred to as the morphology of the DVA. The average elastomericparticle size for the majority of elastomeric particles in the DVA isdefined by a diameter in the range of 100 to 1,000 nanometers (0.1microns to 1.0 microns), or 125 to 500 nanometers in any embodiment ofthe invention, or 125 to 400 nanometers in any embodiment of theinvention. Particle size can be determined by methods well known in theart and including tapping phase atomic force microscopy (AFM). Adetermination of substantial completion of the interfacial reaction canbest be determined by the average elastomeric particle size; if theparticle size is within 50%, or alternatively 70%, or alternatively 75%of the desired final average particle size.

Another key process step is to ensure effective and efficient mixing ofthe rubber and thermoplastic resin. For this, the viscosity of thethermoplastic phase needs to be close to that of the rubber. This isaccomplished by providing a thermoplastic viscosity reducer to the blendat an appropriate point along the extruder, while maintaining an optimalconcentration of thermoplastic to rubber. In the disclosed invention,this is accomplished by delaying addition of all the thermoplastic resininto the feed throat, providing at least a portion of the thermoplasticresin at a location downstream of the rubber feed stream; the lateraddition of thermoplastic resin may occur in more than one downstreamlocation. Furthermore, a reactive plasticizer such as polyisobutylenesuccinic anhydride or polyisobutene succinic anhydride can also be usedto attenuate the viscosity of the thermoplastic phase and may also beadded at multiple locations along the extruder length.

The lower screw speed operation also allows longer residence time whichis needed for completing melting and mixing to complete interfacialreactions and allow cure completion. Another reason for a relativelylower screw speed is to prevent the blend temperature from rising abovethe rubber degradation temperature. The interfacial reactions occurringin the extruder increase the effective molecular weight and viscosity ofthe mixture in the extruder; if the mixture were processed under ahigher screw speed the temperature of this increasingly more viscousmixture would rise above the rubber degradation temperature. Aconsequence of this lower screw speed operation is that the extrudercapacity is limited by available torque or power. This is a significantadvantage to development of a new process where the consumption ofspecific energy (KW-hr/kg) can be reduced.

Elastomers

The elastomeric component of the DVA may be selected from an assortmentof thermosetting, elastomeric materials. For uses where impermeabilityof the final article to be produced is desired, the use of at least onelow-permeability elastomer is desired.

Useful for this invention are elastomers derived from a mixture ofmonomers, the mixture having at least the following monomers: a C₄ to C₇isoolefin monomer and a polymerizable monomer. In such mixtures, theisoolefin is present in a range from 70 to 99.5 wt % of the totalmonomers in any embodiment, or 85 to 99.5 wt % in any embodiment. Thepolymerizable monomer is present in amounts in the range of from 30 toabout 0.5 wt % in any embodiment, or from 15 to 0.5 wt % in anyembodiment, or from 8 to 0.5 wt % in any embodiment. The elastomer willcontain monomer derived unit amounts having the same weight percentages.

The isoolefin is a C₄ to C₇ compound, non-limiting examples of which arecompounds such as isobutylene, isobutene, 2-methyl-1-butene,3-methyl-1-butene, 2-methyl-2-butene, 1-butene, 2-butene, methyl vinylether, indene, vinyltrimethylsilane, hexene, and 4-methyl-1-pentene. Thepolymerizable monomer may be a C₄ to C₁₄ multiolefin such as isoprene,butadiene, 2,3-dimethyl-1,3-butadiene, myrcene, 6,6-dimethyl-fulvene,hexadiene, cyclopentadiene, and piperylene. Other polymerizable monomerssuch as styrene, alkylstyrene e.g., p-methylstyrene, and dichlorostyreneare also suitable for preparing a useful elastomer.

Preferred elastomers useful in the practice of this invention includeisobutylene-based copolymers. An isobutylene based elastomer or apolymer refers to an elastomer or a polymer comprising at least 70 mol %repeat units from isobutylene and at least one other polymerizable unit.The isobutylene-based copolymer may or may not be halogenated.

In any embodiment of the invention, the elastomer may be a butyl-typerubber or branched butyl-type rubber, especially halogenated versions ofthese elastomers. Useful elastomers are unsaturated butyl rubbers suchcopolymers of olefins or isoolefins and multiolefins. Non-limitingexamples of unsaturated elastomers useful in the method and compositionof the present invention are poly(isobutylene-co-isoprene),polyisoprene, polybutadiene, polyisobutylene,poly(styrene-co-butadiene), natural rubber, star-branched butyl rubber,and mixtures thereof. Useful elastomers in the present invention can bemade by any suitable means known in the art, and the invention is notherein limited by the method of producing the elastomer. Butyl rubber isobtained by reacting isobutylene with 0.5 to 8 wt % isoprene, orreacting isobutylene with 0.5 wt % to 5.0 wt % isoprene—the remainingweight percent of the polymer being derived from isobutylene; the butylrubber contains monomer derived unit amounts having the same weightpercentages.

Elastomeric compositions of the present invention may also comprise atleast one random copolymer comprising a C₄ to C₇ isoolefin and analkylstyrene comonomer. The isoolefin may be selected from any of theabove listed C₄ to C₇ isoolefin monomers, and is preferably anisomonoolefin, and in any embodiment may be isobutylene. Thealkylstyrene may be para-methylstyrene, containing at least 80%, morealternatively at least 90% by weight of the para-isomer. The randomcopolymer may optionally include functionalized interpolymers. Thefunctionalized interpolymers have at least one or more of the alkylsubstituents groups present in the styrene monomer units; thesubstituent group may be a benzylic halogen or some other functionalgroup. In any embodiment, the polymer may be a random elastomericcopolymer of a C₄ to C₇ a-olefin and an alkylstyrene comonomer. Thealkylstyrene comonomer may be para-methylstyrene containing at least80%, alternatively at least 90% by weight, of the para-isomer. Therandom comonomer may optionally include functionalized interpolymerswherein at least one or more of the alkyl substituents groups present inthe styrene monomer units contain a halogen or some other functionalgroup; up to 60 mol % of the para-substituted styrene present in therandom polymer structure may be the functionalized. Alternatively, inany embodiment, from 0.1 to 5 mol % or 0.2 to 3 mol % of thepara-substituted styrene present may be the functionalized.

The functional group may be halogen or some other functional group whichmay be incorporated by nucleophilic substitution of any benzylic halogenwith other groups such as carboxylic acids; carboxy salts; carboxyesters, amides and imides; hydroxy; alkoxide; phenoxide; thiolate;thioether; xanthate; cyanide; cyanate; amino and mixtures thereof. Inany embodiment, the elastomer comprises random polymers of isobutyleneand 0.5 to 20 mol % para-methylstyrene wherein up to 60 mol % of themethyl substituent groups present on the benzyl ring is functionalizedwith a halogen such as bromine or chlorine, an acid, or an ester.

In any embodiment, the functionality on the elastomer is selected suchthat it can react or form polar bonds with functional groups present inthe thermoplastic resin, for example, acid, amino or hydroxyl functionalgroups, when the DVA components are mixed at reactive temperatures.

Brominated poly(isobutylene-co-p-methylstyrene) “BIMSM” polymers usefulin the present invention generally contain from 0.1 to 5 mol % ofbromomethylstyrene groups relative to the total amount of monomerderived units in the copolymer. In any embodiment of the invention usingBIMSM, the amount of bromomethyl groups is from 0.5 to 3.0 mol %, orfrom 0.3 to 2.8 mol %, or from 0.4 to 2.5 mol %, or from 0.5 to 2.0 mol%, wherein a desirable range for the present invention may be anycombination of any upper limit with any lower limit. Also in accordancewith the invention, the BIMSM polymer has either 1.0 to 2.0 mol %bromomethyl groups, or 1.0 to 1.5 mol % of bromomethyl groups. Expressedanother way, exemplary BIMSM polymers useful in the present inventioncontain from 0.2 to 10 wt % of bromine, based on the weight of thepolymer, or from 0.4 to 6 wt % bromine, or from 0.6 to 5.6 wt %. UsefulBIMSM polymers may be substantially free of ring halogen or halogen inthe polymer backbone chain. In any embodiment, the random polymer is apolymer of C₄ to C₇ isoolefin derived units (or isomonoolefin),para-methylstyrene derived units and para-(halomethylstyrene) derivedunits, wherein the para-(halomethylstyrene) units are present in thepolymer from 0.5 to 2.0 mol % based on the total number ofpara-methylstyrene, and wherein the para-methylstyrene derived units arepresent from 5 to 15 wt %, or 7 to 12 wt %, based on the total weight ofthe polymer. In any embodiment, the para-(halomethylstyrene) ispara-(bromomethylstyrene).

Other suitable low-permeability elastomers are isobutylene containingelastomers such isobutylene-isoprene-alkylstyrene terpolymers orhalogenated isobutylene-isoprene-alkylstyrene terpolymers wherein foreach of these terpolymers, the isobutylene derived component in theterpolymer is 70 to 99 wt % of the monomer units in the polymer, theisoprene derived component is 29 to 0.5 wt % of the monomer units in thepolymer, and the alkylstyrene derived component is 29 to 0.5 wt % of themonomer units in the polymer.

Suitable C₄ to C₇ isoolefin derived elastomers (including the brominatedisobutylene-paramethylstyrene copolymers) having a number averagemolecular weight Mn of at least about 25,000, preferably at least about50,000, preferably at least about 75,000, preferably at least about100,000, preferably at least about 150,000. The polymers may also have aratio of weight average molecular weight (Mw) to number averagemolecular weight (Mn), i.e., Mw/Mn of less than about 6, preferably lessthan about 4, more preferably less than about 2.5, most preferably lessthan about 2.0. In another embodiment, suitable halogenated isobutyleneelastomer components include copolymers (such as brominatedisobutylene-paramethylstyrene copolymers) having a Mooney viscosity(1+4) at 125° C. (as measured by ASTM D 1646-99) of 30 or more, or morepreferably 40 or more.

Preferred elastomers include copolymers of isobutylene andpara-alkylstyrene, which may or may not be halogenated. Preferably thecopolymer of isobutylene and para-alkylstyrene is halogenated. Suchelastomers are described in European Patent Application 0 344 021. Thecopolymers preferably have a substantially homogeneous compositionaldistribution. Preferred alkyl groups for the para-alkylstyrene moietyinclude alkyl groups having from 1 to 5 carbon atoms, primary haloalkyl,secondary haloalkyl having from 1 to 5 carbon atoms and mixturesthereof. A preferred copolymer comprises isobutylene andpara-methylstyrene. Preferred brominated copolymers of isobutylene andpara-methylstyrene include those having 5 to 12 weight %para-methylstyrene, 0.3 to 1.8 mol % brominated para-methylstyrene, anda Mooney viscosity of 30 to 65 (1+4) at 125° C. (as measured by ASTM D1646-99).

Thermoplastic Resin

For purposes of the present invention, a thermoplastic (alternativelyreferred to as thermoplastic resin) is a thermoplastic polymer,copolymer, or mixture thereof having a Young's modulus of more than 200MPa at 23° C. The resin should have a melting temperature of about 160°C. to about 260° C., preferably less than 260° C., and most preferablyless than about 240° C. In a preferred embodiment, the thermoplasticresin should have a molecular weight in the range of 13,000 to 50,000.By conventional definition, a thermoplastic is a synthetic resin thatsoftens when heat is applied and regains its original properties uponcooling.

Such thermoplastic resins may be used singly or in combination andgenerally contain nitrogen, oxygen, halogen, sulfur or other groupscapable of interacting with an aromatic functional groups such ashalogen or acidic groups. Suitable thermoplastic resins include resinsselected from the group consisting or polyamides, polyimides,polycarbonates, polyesters, polysulfones, polylactones, polyacetals,acrylonitrile-butadiene-styrene resins (ABS), polyphenyleneoxide (PPO),polyphenylene sulfide (PPS), polystyrene, styrene-acrylonitrile resins(SAN), styrene maleic anhydride resins (SMA), aromatic polyketones(PEEK, PED, and PEKK), ethylene copolymer resins (EVA or EVOH) andmixtures thereof.

Suitable polyamides (nylons) comprise crystalline or resinous, highmolecular weight solid polymers including homopolymers, copolymers, andterpolymers having recurring amide units within the polymer chain.Polyamides may be prepared by polymerization of one or more epsilonlactams such as caprolactam, pyrrolidione, lauryllactam andaminoundecanoic lactam, or amino acid, or by condensation of dibasicacids and diamines Both fiber-forming and molding grade nylons aresuitable. Examples of polyamides include polycaprolactam (nylon-6),polylauryllactam (nylon-12), polyhexamethyleneadipamide (nylon-6,6),polyhexamethyleneazelamide (nylon-6,9), polyhexamethylenesebacamide(nylon-6,10), poly(hexamethylene dodecanediamide (nylon-6,12),polyhexamethyleneisophthalamide (nylon-6, IP) and the condensationproduct of 11-amino-undecanoic acid (nylon-11). Commercially availablepolyamides may be advantageously used in the practice of this invention,with linear crystalline polyamides having a softening point or meltingpoint between 160 and 260° C. being preferred.

Suitable polyesters which may be employed include the polymer reactionproducts of one or a mixture of aliphatic or aromatic polycarboxylicacids esters of anhydrides and one or a mixture of diols. Examples ofsatisfactory polyesters include poly(trans-1,4-cyclohexylene C₂₋₆ alkanedicarboxylates such as poly(trans-1,4-cyclohexylene succinate) andpoly(trans-1,4-cyclohexylene adipate); poly(cis ortrans-1,4-cyclohexanedimethylene)alkanedicarboxylates such aspoly(cis-1,4-cyclohexanedimethylene)oxlate andpoly-(cis-1,4-cyclohexanedimethylene)succinate, poly(C₂₋₄ alkyleneterephthalates) such as polyethyleneterephthalate andpolytetramethylene-terephthalate, poly (C₂₄ alkylene isophthalates) suchas polyethyleneisophthalate and polytetramethylene-isophthalate and likematerials. Preferred polyesters are derived from aromatic dicarboxylicacids such as naphthalenic or phthalic acids and C₂ to C₄ diols, such aspolyethylene terephthalate and polybutylene terephthalate. Preferredpolyesters will have a melting point in the range of 160° C. to 260° C.

Poly(phenylene ether) (PPE) resins which may be used in accordance withthis invention are well known, commercially available materials producedby the oxidative coupling polymerization of alkyl substituted phenols.They are generally linear, amorphous polymers having a glass transitiontemperature in the range of 190° C. to 235° C.

Ethylene copolymer resins useful in the invention include copolymers ofethylene with unsaturated esters of lower carboxylic acids as well asthe carboxylic acids per se. In particular, copolymers of ethylene withvinylacetate or alkyl acrylates for example methyl acrylate and ethylacrylate can be employed. These ethylene copolymers typically compriseabout 60 to about 99 wt % ethylene, preferably about 70 to 95 wt %ethylene, more preferably about 75 to about 90 wt % ethylene. Theexpression “ethylene copolymer resin” as used herein means, generally,copolymers of ethylene with unsaturated esters of lower(C₁-C₄)monocarboxylic acids and the acids themselves; e.g., acrylicacid, vinyl esters or alkyl acrylates. It is also meant to include both“EVA” and “EVOH”, which refer to ethylene-vinylacetate copolymers, andtheir hydrolyzed counterpart ethylene-vinyl alcohols.

In the dynamically vulcanized alloy, the thermoplastic resin is presentin an amount ranging from about 10 to 98 wt % based on the alloy blend,and from about 20 to 95 wt % in another embodiment. In yet anotherembodiment, the thermoplastic resin is present in an amount ranging from35 to 90 wt %. The amount of elastomer in the DVA is in an amountranging from about 2 to 90 wt % based on the alloy blend, and from about5 to 80 wt % in another embodiment. In any embodiment of the invention,the elastomer is present in an amount ranging from 10 to 65 wt %. In theinvention, the thermoplastic resin is present in the alloy, relative tothe amount of elastomer, in an amount in the range of 40 to 80 phr.

Secondary Elastomer

In some embodiments, the DVA may further comprise a secondary elastomer.The secondary elastomer may be any elastomer, but preferably thesecondary elastomer is not an isobutylene-containing elastomer. Anexample of a preferred secondary elastomer is a maleicanhydride-modified copolymer. Preferably, the secondary elastomer is acopolymer comprising maleic anhydride and ester functionalities such asmaleic anhydride-modified ethylene-ethyl acrylate.

The secondary elastomer may be added to the DVA processing extrudersimultaneously with the initial elastomer and the thermoplastic resininitial feedstreams. Alternatively, it may be added to the extruderdownstream from the elastomer and initial thermoplastic resinfeedstreams.

The amount of the secondary elastomer in the DVA may be in the range offrom about 2 wt % to about 45 wt %. If the DVA comprises at least oneelastomer and a secondary elastomer, the total amount of both theelastomer and secondary elastomer is preferably in the range of fromabout 2 wt % to about 90 wt %.

This secondary elastomer may be cured along with the primary isoolefinbased elastomer or it may be selected to remain uncured and act as acompatibilizer as discussed below.

Other DVA Components

Other materials may be blended into the DVA to assist with preparationof the DVA or to provide desired physical properties to the DVA. Suchadditional materials include, but are not limited to, curatives,stabilizers, compatibilizers, reactive plasticizers, non-reactiveplasticizers, extenders and polyamide oligomers or low molecular weightpolyamide and other lubricants as described in U.S. Pat. No. 8,021,730B2.

Curing of the primary elastomer is generally accomplished by theincorporation of the curing agents and optionally accelerators, with theoverall mixture of any such components referred to as the cure system orcure package. Suitable curing components include sulfur, metal oxides,organometallic compounds, radical initiators. Common curatives includeZnO, CaO, MgO, Al2O3, CrO3, FeO, Fe2O3, and NiO. These metal oxides canbe used alone or in conjunction with metal stearate complexes (e.g., thestearate salts of Zn, Ca, Mg, and Al), or with stearic acid or otherorganic acids and either a sulfur compound or an alkyl or aryl peroxidecompound or diazo free radical initiators. If peroxides are used,peroxide co-agent commonly used in the art may be employed. The use ofperoxide curative may be avoided if the thermoplastic resin is one suchthat the presence of peroxide would cause the thermoplastic resin tocross-link.

As noted, accelerants (also known as accelerators) may be added with thecurative to form a cure package. Suitable curative accelerators includeamines, guanidines, thioureas, thiazoles, thiurams, sulfenamides,sulfenimides, thiocarbamates, xanthates, and the like.

Numerous accelerators are known in the art and include, but are notlimited to, the following: stearic acid, diphenyl guanidine (DPG),tetramethylthiuram disulfide (TMTD), 4,4′-dithiodimorpholine (DTDM),tetrabutylthiuram disulfide (TBTD), 2,2′-benzothiazyl disulfide (MBTS),hexamethylene-1,6-bisthiosulfate disodium salt dihydrate,2-(morpholinothio)benzothiazole (MBS or MOR), compositions of 90% MORand 10% MBTS (MOR90), N-tertiarybutyl-2-benzothiazole sulfenamide(TBBS), N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), andN-oxydiethylene thiocarbamyl-N-oxydiethylene sulfonamide (OTOS), zinc2-ethyl hexanoate (ZEH), N,N′-diethyl thiourea.

In any embodiment of the invention, at least one curing agent istypically present at about 0.1 to about 15 phr; alternatively at about1.0 to about 10 phr, or at about 1.0 to 6.0 phr, or at about 1.0 to 4.0phr, or at about 1.0 to 3.0 phr, or at about 1.0 to 2.5 phr, or at about2.0 to 5.0 phr. If only a single curing agent is used, it is preferablya metal oxide such as zinc oxide.

Minimizing the viscosity differential between the elastomer and thethermoplastic resin components during mixing and/or processing enhancesuniform mixing and fine blend morphology that significantly enhance goodblend mechanical as well as desired permeability properties. However, asa consequence of the flow activation and shear thinning characteristicinherent in elastomeric polymers, reduced viscosity values of theelastomeric polymers at the elevated temperatures and shear ratesencountered during mixing are much more pronounced than the reductionsin viscosity of the thermoplastic component with which the elastomer isblended. It is desired to reduce this viscosity difference between thematerials to achieve a DVA with acceptable elastomeric dispersion sizes.

Components previously used to compatibilize the viscosity between theelastomer and thermoplastic components include low molecular weightpolyamides, maleic anhydride grafted polymers having a molecular weighton the order of 10,000 or greater, methacrylate copolymers, tertiaryamines and secondary diamines. One common group of compatibilizers aremaleic anhydride-grafted ethylene-ethyl acrylate copolymers (a solidrubbery material available from Mitsui-DuPont as AR-201 having a meltflow rate of 7 g/10 min measured per JIS K6710), as well asbutylbenzylsulfonamide and polyisobutylene succinic anhydride; the useof such additives are further discussed in pending U.S. application Ser.No. 12/548,797, filed Aug. 29, 2009. These compounds may act to increasethe ‘effective’ amount of thermoplastic material in theelastomeric/thermoplastic compound. The amount of additive is selectedto achieve the desired viscosity comparison without negatively affectingthe characteristics of the DVA. If too much additive is present,impermeability may be decreased and the excess may have to be removedduring post-processing. If not enough compatibilizer is present, theelastomer may not invert phases to become the dispersed phase in thethermoplastic resin matrix.

Both reactive and non-reactive plasticizers can function ascompatibilizers due to the nature of a plasticizer. Plasticizers forthermoplastics are generally defined as a compound added to polymericmaterials to improve flexibility, extensibility, and processability.Known and conventional thermoplastic plasticizers are supplied in theform of low to high viscosity liquid and may be functionalized. Manydifferent plasticizers are known in the thermoplastic resin art asplasticizers have different compatibilities with each type ofthermoplastic resin and have different effects on the properties of thethermoplastic resin. Known thermoplastic plasticizers include differenttypes of esters, hydrocarbons (aliphatic, naphthenic, and aromatic),polyesters, and polycondensates; see Handbook of ThermoplasticElastomers, Jiri George Drobny, p. 23 (William Andrew Publishing, 2007).For polyamides, known non-reactive plasticizers include hydrocarbonsfunctionalized by tertiary amines, secondary diamines, or sulfonamides.One particularly well known compound is butylbenzylsulfonamide (BBSA).

Both maleic and succinic anhydrides functionalized oligomers are alsouseful as reactive plasticizers. The anhydride functionalized oligomer(AFO) may be prepared by thermal or chloro methods known in the art ofreacting an alkyl, aryl, or olefin oligomer with anhydride, preferablymaleic anhydride. The oligomer of any embodiment of the invention,including copolymers of lower olefins, being reacted with the anhydride,has a molecular weight in the range of about 500 to 5000, or 500 to2500, or 750 to 2500, or 500 to 1500. The oligomer of the invention mayalso have a molecular weight in the ranges of 1000 to 5000, 800 to 2500,or 750 to 1250. Specific examples of succinic anhydrides includepoly-isobutylene succinic anhydride, poly-butene succinic anhydride,n-octenyl succinic anhydride, n-hexenyl succinic anhydride, anddodocenyl succinic anhydride. The most preferred anhydridefunctionalized oligomers for this invention are those derived frompolyisobutene and are commonly known as polyisobutylene succinicanhydride or polyisobutene succinic anhydride (PIBSA). The PIBSA may bemade by cationic polymerization of isobutene with boron trifluoride ascatalyst. In the course of the polymerization, high concentrations ofa-olefins are formed during the transfer reaction and as a result thepolymerization product has a high proportion of terminal double bonds(α-olefin). They are normally clear to amber viscous liquids and arespecially optimized during the post polymerization maleation reaction tohave a low bismaleiation.

The anhydride level of the AFO of the invention may vary and a preferredrange is about 1 to about 30 wt % with a preferred range of 5 to 25 wt %and a more preferred range of 7 to 17 wt % and a most preferred range of9 to 15 wt %.

DVA Mixing

Previously, a variety of mixers and combinations of mixers have beenconsidered suitable for preparing DVAs. However, the morphology of theDVA is dependent upon the mixing conditions, including temperature,order of introducing ingredients, residence time, as well as shearrates. For thin films, of the type to be used for preparing tire innerliners, the morphology of the DVA is critical in obtaining the desiredproperties. Uniform distribution of submicron or nanometer sizedelastomer particles in a continuous polyamide matrix is important toachieve optimum properties. In particular, for these DVA end-useapplications, the timing of the addition of the curing components andthe temperature profile of the various components during mixing arecritical to ensure the correct morphology is developed. Sub-inclusionsof the thermoplastic inside the rubber particles may also be present;but for any sub-inclusions in the elastomer, the thermoplastic resinwill preferably not be discontinuous in the DVA. Thus, prior methods ofDVA preparation are being found insufficient to meet more stringentmorphology and property demands for the DVA.

As discussed already, to obtain the desired morphology, Applicants havedetermined that several key reactions must occur in proper order and keyprocess factors must be considered during mixing.

An embodiment of the invention will now be more particularly describedwith reference to FIG. 1. A twin screw extruder 10 is the preferred meltprocessing device (those in the art will appreciate that the drawing ismerely schematic of a twin screw extruder and is not limited for anyactual extruder; i.e., open or closed feed points). The extruder 10preferably has at least two intermeshing and co-rotating screws 12located along the length of the extruder 10. At one end of the extruder10 is a feed throat 14 into which flows at least two feedstreams: aprimary thermoplastic resin feedstream 16 and an elastomer feedstream18. Neither the resin nor the elastomer in these feedstreams 16, 18 havebeen preblended (beyond that which was necessary to obtain theelastomeric copolymer or thermoplastic polymer or copolymer) or preparedas a masterbatch prior to entry into the extruder 10. The elastomer hasbeen chopped into granulate form and coated with minimal amounts of apartitioning agent, such as talc, to enable the elastomer to be freeflowing as it enters the extruder 10 but it has not been blended withany curatives, fillers, or other compounding additives. At the initialfeed throat 14, optional additional feedstreams may be introduced intothe extruder 10 in any combination with the thermoplastic and elastomerfeedstreams 16, 18: a plasticizer or compatibilizer feedstream 20, asecondary thermoplastic resin and/or elastomer feedstream 22, and astabilizer feedstream 24. The stabilizer fed into the extruder 10 viathe feedstream 24 may be a pelletized form of the desired stabilizer inthe DVA composition that has been preblended into a small amount of theprimary thermoplastic resin. Alternatively, all of these feed streamsmay be blended just before being feed into the extruder via the initialfeed throat 14.

The amount of the primary thermoplastic resin added to the extruder 10via feedstream 16 is preferably less than the total amount of primarythermoplastic resin intended to be present in the final DVA composition.As noted above, by delaying the addition of all the thermoplastic resininto the mixture, an optimal concentration of thermoplastic to rubber isobtained while initial interfacial grafting between the thermoplasticand the rubber occurs. This also slows down an undesirable significantincrease in the viscosity of the mixture as it flows thru the firstportion of the extruder 10. In fact, it could be inferred that thereduction in thermoplastic viscosity that aids the mixing of thethermoplastic and elastomer also promotes the interfacial reactionbetween these components.

The temperature in the first half of the extruder 10 reaches atemperature of 5° C. to 45° C. above the melt temperature of thethermoplastic resin. For the majority of the above listed thermoplasticresins, including the preferred polyamide resins, this is a temperaturerange of 230° C. to 270° C. During mixing of the elastomer and thethermoplastic resin in the first half of the extruder 10, due tointerfacial reaction of the thermoplastic resin and elastomer, themolecular weight and viscosity of the mixture begins to increase. Tocontrol this viscosity increase of the mixture, downstream of theinitial feedthroat 14, compatibilizer or viscosity modifier may beintroduced via at least one new feedstream 26. Applicants also theorizethat the delay in addition of all of the thermoplastic resin results inan optimal concentration of thermoplastic to plasticizer to reduce thethermoplastic viscosity to that of, or just below, the elastomer topromote mixing to achieve the desired morphology. When the feedstream 26is introduced as a liquid feedstream, metering pumps are used to ensurethe correct pressure and amount of liquid is added to the extruder 10.For a liquid stream, the compatibilizer is added at an injectionpressure between 0 to 700 psi. This addition of compatibilizer is addedbefore curatives are added, so that the viscosity of the mixture duringprogress of the interfacial reaction is controlled. In one embodiment,all of the compatibilizer or plasticizer is added in the initial feedthroat 14, thereby initially maximizing the ‘effective’ amount of thethermoplastic resin and decreasing the resin viscosity; this makes itpossible to achieve an improved phase inversion of the elastomer andresin during mixing of the DVA.

The feedstream 26 is introduced at a point anywhere from 15% of theextruder length to 38% of the extruder length to diameter ratio (L/D).The L/D ratio is in the range of 30 to 80, or 36 to 72, or alternatively40 to 60. The length L typically refers to the flighted length of thescrew; in other words, the length of the screw portion that containsflights. If flights are present on the screw in a portion which does notencounter the components of the composition, such portion is notincluded in the determination of the screw length L. The diameter D ofthe screw refers to the maximum width of the bore in the extruderbarrel, into which the flighted screw fits; in other words where screwflights are present, since extruder screws typically have sections ofvarying width depending on the function of a particular portion of thescrew. If flights are present on the screw in a portion which does notencounter the components of the composition, such a portion is notincluded in the determination of screw length of extruder. Onceestablished for a given system/composition, the L/D ratio is typically amaintained constant even if the extruder size is changed. In anyembodiment of the invention the feedstream 26 may be located anywherefrom 15% to 35% of the extruder L/D. The addition point of feed stream26 is after the initial feedthroat 14 but before the addition of anycurative/vulcanization components. If the introduction is too soon,sufficient time for initiation of the interfacial reaction might not beprovided. However, if the compatibilizer feedstream is after 38% of theextruder length, the mixture may be too viscous to obtain good dispersalof the later added curatives or successful phase inversion of the rubberand thermoplastic resin.

After sufficient mixing of the elastomer and the thermoplastic resin toobtain grafting of the rubber and thermoplastic resin, the seconddesired reaction, vulcanization of the rubber, is initiated via analready added long induction time curative or curatives added into theextruder 10. The curatives may be added as a powder, a liquid, or asolid. In any embodiment of the invention, all of the curatives to beused may be preblended in a single form, such as a solid pellet.Alternatively, all or some of the curatives may be preblended with apre-determined measure of thermoplastic resin to form a curativepre-blend. In such embodiments, the amount of thermoplastic resin usedto form the curative pre-blend will be not more than 15 wt % of thetotal amount of thermoplastic resin used in the final DVA composition;preferably not more than 10 wt %, more preferably not more than 8 wt %.Thus, at least some of the curatives are pre-blended with 0 to 15 wt %of the total amount of thermoplastic resin, or from 0 to 10 wt % or 0 to8 wt % of the total amount of thermoplastic resin. The thermoplasticresin used to preblend with the curatives may be the primary or asecondary thermoplastic resin; for example, if the DVA composition usesboth a primary nylon copolymer and a secondary nylon homopolymer, thecurative preblend may incorporate either the copolymer or thehomopolymer. The curatives are added via a feedstream 28 at feedthroat30 of the extruder. The feedthroat 30, and thus the introduction of thecurative feedstream 28, may be at any point from 30% to 60% of theextruder length L/D. Alternatively, in any embodiment of the invention,the feedstream 28 may be introduced into the extruder at any point from33% to 45% of the extruder length L/D.

Additionally, at feedthroat 30, additional thermoplastic resinfeedstream 32 enters the extruder 10. The two feedstreams 28, 32 may beblended together using an additional mixer prior to entering thefeedthroat 30 or as discussed above; or the streams 28, 32 may be addedat any point within the permissible feedthroat 30 location along theextruder length as discussed above. The total amount of additionalthermoplastic resin, whether added via feedstream 32 and/or preblendedwith the curatives, is in the range of 10 to 75 wt %, alternatively 25to 70 wt %, alternatively 30 to 65 wt %, alternatively 30 to 55 wt %, oralternatively not less than 10 wt % of the total amount of thermoplasticresin used in the final DVA composition. In any embodiment of theinvention, this secondary addition of thermoplastic resin should be notmore than 75 wt % of the total amount of thermoplastic resins in theDVA. After this downstream addition of this portion of thermoplasticresin, all of the thermoplastic resin required for the DVA compositionhas been introduced into the extruder. The downstream addition, orsecond portion addition, of thermoplastic resin may be the primarythermoplastic resin or a secondary thermoplastic resin in the DVAcomposition. This downstream addition is accomplished via a non-melt ormelt feed apparatus.

After the introduction of the curatives 28 and the secondary addition ofprimary thermoplastic, the temperature in the extruder 10 is reduced by5° C. to 50° C. to achieve a temperature in the range of 225° C. to 260°C. This reduction in extruder temperature is to enable curing of thedispersed particles of elastomer in the mixture; however, the maximumtemperature is determined to prevent scorching of the elastomer. Thetemperature in the extruder 10 at this point enables curing of theelastomer in a controlled manner so that the elastomer achieves thedesired cure profile. Several cure profiles are shown in FIG. 2. Thesecure profiles are obtainable in the extruder 10, wherein the step-growthcure profile [shown by the solid symbols] is a preferred cure profile.With the step-growth cure profile, the DVA exits the extruder 10substantially fully cured and is less subject to reversion of the cureduring subsequent use of the DVA in film forming and article formingapplications.

After curing of the elastomer has begun, at a location downstream of thefeedthroat 30 additional constituents 34 of the DVA may be introducedinto the extruder 10. Such additional constituents may include, but arenot limited to, thermal and/or UV stabilizers and additional viscositymodifiers such as the already discussed AFOs. At such a downstreamlocation, due to the curing—and polymer chain movement restriction dueto the curing—the addition of a viscosity modifier at a downstreamlocation is helpful to continue to move the DVA through the extruder.Viscosity modifiers and stabilizers may include 6PPD, steric acid, andlow molecular weight nylon blends. Addition could be one or more ofthese additives at 0% to 5%, preferably at 0.5% to 3%, more preferablyat 0.5% to 2%. The feed of such additional constituents 34 can beprovided in neat format as a solid or a liquid or as a concentrate insolid or liquid form. A liquid form may be preferred if the additiveshave a lower melt point than the melt temperature in the mixer at theaddition point to prevent blockage in the feeder or extruder due to anyundesired isolated melting of the additives.

Any volatiles or gasses generated during mixing may be removed using avacuum vent at one or more locations (not illustrated) along theextruder 10; such vacuum vents or gas ports are well known in theextruder art. Excess zinc oxide present will also act as an acidscavenger and neutralize any hydrogen halide gas.

After the DVA has been mixed to form the alloy, in any embodiment of theinvention, the DVA exits the extruder 10 and passes through a melt gearpump in preparation for sending the DVA through downstream operationssuch as a pelletizing extruder.

One of the control conditions for the extrusion mixing is specificenergy, which is equivalent to the overall energy supplied to theextruder per the mass passing through the extruder. The amount ofoverall energy supplied to the material may be affected by the melttemperature in the extruder, the amount of energy required to rotate theextruder blocks in the extruder, the amount of mass moving through theextruder, and the speed of the mass moving through the extruder. Forexample, if a small volume of mass having a low viscosity and a low melttemperature is moved through an extruder, not much energy is required tomove the material through the extruder. Stated conversely, depending onthe material selection, lower screw speeds require lower energy torotate the screws, and a lower temperature is generated in the melt. Dueto this relationship, the RPM of the screw may be proportional to themelt temperature; thus, for higher viscosity mixes with higher melttemperatures a greater amount of energy is required for a given screwdesign.

Another control condition for the preparation of the DVA is the shearrate to which the DVA materials are subjected during extrusion. Theshear rate for the extruder is calculated as:

Shear rate, sec⁻¹=(π·extruder diameter−screw speed)/screw clearance

Shear rate is typically independent of equipment size, permittingvarious size extruders to be used to obtain the DVA. For the presentinvention, the shear rate is in the range of 7500 sec⁻¹ to 50 sec⁻¹; oralternatively in the range of 5750 sec⁻¹ to 65 sec⁻¹ or in the range of5000 sec⁻¹ to 100 sec⁻¹ or in the range of 4750 to 500 sec⁻¹. When shearrate is multiplied by the residence time (equivalent to rate/freevolume) of the material in the extruder, the shear strain per RPM of themachine can be determined and this value can be used for scale upindependent of machine size when preparing materials. The residence timeof the present invention is in the range of 60 seconds to 600 seconds,measured from the initial extruder feedthroat 14 to the discharge of thepellets from the pelletizer; when measured from the feedthroat 14 to theextruder end, the residence time is in the range of 30 seconds to 500seconds.

The capacity or rate of the extruder 10 is proportional to the extrudersize and screw speed for any given extruder screw design. For thepresent invention, the capacity of the extruder is preferably 30 kg/hrto a maximum 150 kg/hr for an extruder having a 40 to 200 RPM speed witha maximum diameter of up to 320 mm. In any embodiment of the presentinvention, the screw has a maximum diameter in the range of 40 mm to 150mm or alternatively 40 mm to 100 mm. The capacity may be scaled up forlarger diameter extruders using the following equation:

Extruder 2 capacity=[extruder 1 capacity]·(diameter extruder 2/diameterextruder 1)^(2.7)

This capacity is reduced from that conventionally used for thermoplasticvulcanizates. This is specific to this type of DVA wherein themorphology of the DVA is critical to achieving the desired performancein the intended end use of a tire innerliner.

While FIG. 1 illustrates a twin screw extruder, the present inventionmay be practiced on an extruder that has more than two screws, and mayalso be practiced on a ring screw extruder of the type disclosed in U.S.Pat. No. 7,655,728 so long as the extruder has been set up or modifiedto achieve the above described addition sequence, specific energy, andshear rates.

During the dynamic vulcanization process, several key competingreactions/mechanisms occur. The first is the reaction between thethermoplastic resin and the elastomer. For example, a component of thethermoplastic, such as the amine group of polyamide, may react with thependant halogen of a halogenated elastomer. This interfacial graftingreaction results in a high viscosity elastomer copolymer. Meanwhile,physical mechanisms may occur due to the shear mixing, such as anerosion phenomenon and other conventional drop breakup mechanism such ascapillary drop break-up. The edge portions of rubber which are graftedwith the thermoplastic resin are pulled away from the main rubberparticle body during the shear mixing and elongation flowing of thecopolymer. If the DVA is heated too much due to excessive energy ortemperature applied to the system, cross-linking of the elastomer mayactually slow down the erosion phenomenon and other conventional dropbreakup mechanisms, and reduce the ability of the elastomer to be finelydispersed within the DVA.

The interfacial grafting reaction and the shear mixing allow for a DVAhaving a fine dispersion of elastomer as small particles in thecontinuous nylon phase. In the processing of the DVA, especially thoseblends containing a majority of elastomer, in the early stages ofmixing, as the elastomer and the thermoplastic resin are meltedtogether, the lower softening-temperature elastomer and thethermoplastic resin form a co-continuous morphology and may evidencethermoplastic resin particles. As the interfacial grafting reactionoccurs the interfacial tension is lowered, allowing the two phases tobecome compatible. During curing, the elastomer phase is dispersed andit becomes a discontinuous phase dispersed in the continuous phase ofthermoplastic resin. The dynamically vulcanized elastomer is preferablydispersed in the thermoplastic resin matrix in the form of smallparticles having an average particle size of not more than 1 micron, orin the alternative ranges of about 0.1 micron to about 1 micron, orabout 0.1 micron to about 0.75 micron, or about 0.1 micron to about 0.5micron. Particle size can be determined by methods well known in the artand including tapping phase atomic force microscopy (AFM).

As already noted, the process by which the DVA is produced impacts themorphology of the DVA. The inventive process improves the morphology ofthe DVA over that which is achieved during prior conventionalmasterbatch mixing processes or prior twin-screw extruder operations.Due to the curative not being in the rubber as in the former masterbatchprocess the interfacial reaction is effectively decoupled from thecuring reaction which in this inventive one-step process beginsprimarily at the point of curative addition and thereafter and thereforesubsequent to the interfacial grafting reaction. The morphology of theDVA can be reflected by particular properties of the DVA film, includingcapillary viscosity and extrusion surface roughness, or determined byanalytical tools such as atomic force microscopy.

EXAMPLES

The inventive process for manufacturing DVAs will now be furtherdescribed with reference to the following non-limiting examples.

When possible, standard ASTM tests were used to determine the DVA'sphysical properties.

The elastic shear modulus (G′) is measured as the ratio of the shearstress over shear strain of the DVA. G′ value of the DVA can affect theperformance of the resultant tire prepared. G′ is measured in kPa and ismeasured in the solid state according to ASTM D7605 at 1% strain at 100°C. using sub test Strain 05. Preferably, the G′ of the DVA of theinvention is greater than about 4,500 or 5,000 kPa to less than about7,000 or 7,500 kPa.

The elastic stiffness modulus (S′) is measured in dNm according to ASTMD7605 at 200% strain at 215° C. using sub test Strain 02. Preferably,the S′ of the DVA of the invention is greater than about 4 dNm to less 7dNm, or in the range of 5 to 7 dNm.

Oxygen permeability was measured using a MOCON OxTran Model 2/61operating under the principle of dynamic measurement of oxygen transportthrough a thin film. The units of measure are cc-mm/m²-day-mmHg.Generally, the method is as follows: flat film or rubber samples areclamped into diffusion cells which are purged of residual oxygen usingan oxygen free carrier gas. The carrier gas is routed to a sensor untila stable zero value is established. Pure oxygen or air is thenintroduced into the outside of the chamber of the diffusion cells. Theoxygen diffusing through the film to the inside chamber is conveyed to asensor which measures the oxygen diffusion rate. Permeability was testedby the following method. Thin, vulcanized test specimens from the samplecompositions were mounted in diffusion cells and conditioned in an oilbath at 60° C. The time required for air to permeate through a givenspecimen is recorded to determine its air permeability. Test specimenswere circular plates with 12.7-cm diameter and 0.38-mm thickness. Theerror (2σ) in measuring air permeability is ±0.245(×10⁸) units. Alisting of various components used in the DVA samples is provided inTable 1.

TABLE 1 Various Components in the DVA Material Brief DescriptionCommercial Source BIMSM 1 5 wt % PMS, 0.75 mol % BrPMS, Mooney viscosityof 45 ± 5 MU (1 + 8, 125° C.) ZnO Zinc Oxide Kadox 911 Zinc Corp.Stearic Acid Stearic Fatty Acid F1000; Harwick ZnSt Zinc Stearate WitcoChemtura/Crompton Talc UltraTalc 609; Mineral Technologies Polyamide 180 wt % PA6/20 UBE 5024; UBE Chemical wt % PA66 Polyamide 2 100 wt % PA6Ultramid B27; BASF Antioxidant 1 Irganox 1098; Ciba Antioxidant 2Tinuvin 622LD; Ciba Antioxidant 3 Copper Iodide Sigma-Aldrich PIBSAPolyisobutylene succinic PIBSA 950 from Texas anhydride, MW beforePetrochemicals LP anhydride reaction = 950, Or Dovermulse H1000viscosity at 100° C. = 459 from Dover Chemical cSt, saponification # =Corp. 100 mg KOH/gm Compatibilizer Pentaerythritol Tetrasterate Aflux54; Rhein-Chemie

Table 2 shows the composition and tested properties of Samples 1-19. Thesamples were prepared by the process for preparing DVAs disclosedherein. Specifically, a rubber master batch was first mixed using abatch internal mixer. The elastomeric masterbatch is also‘accelerated’—meaning the curative is preblended with the elastomer inthe batch mixer at a temperature below cure initiation temperature ofthe rubber. After the rubber master batch was mixed it was introducedinto a rubber granulator. A thermoplastic resin master batch was mixedusing a twin screw extruder and then pelletized. Then the granulatedrubber master batch, the compatibilizer, and the pelletized resinmasterbatch were then fed into the DVA processing twin screw extruderhaving co-rotating fully intermeshing flights. This process is known as‘dual masterbatching’. DVA's prepared by the older masterbatching methodmay be subject to reversion/degredation of the elastomer if theelastomer masterbatch is prepared too far in advance of preparation ofthe DVA. Table 2 provides the amount of the respective DVA component, asdetailed in Table 1, in terms of parts per hundred rubber. In thesesamples, in terms of wt % of the DVA, the BIMSM elastomer is present at53-56 wt % and the primary thermoplastic resin, the polyamide copolymer,is present in an amount of 30.91 wt %, and the plasticizer is present inan amount of 13.25 wt %.

Table 2 also provides properties of the DVA, including G′, S′, andtemperature of extruder barrel sections 7 through 11. As the Samplesindicate, a target G′ of the DVA can be achieved by modifying theprocess conditions, e.g., process temperature and extruder screw design,and/or product conditions, e.g., amount and type of curatives used toprepare the DVA and amount of thermoplastic resin. A G′ above 7,500 kPamay result in cracks in the tire prepared using the DVA and poor rollingresistance. A G′ below 4,500 kPa may result in difficult processingconditions for the DVA filmed prepared thereof. The inventors havediscovered that preparing a film with a DVA (having a defined G′ and S′value), via the disclosed one-step process, results in improvedperformance properties of the resultant tire/tire application.

TABLE 2 1 2a 2b 3a 3b 3c 4a 4b 4c BIMSM 1 100 100 100 100 100 100 100100 100 ZnO 2 3 3 2 2 2 2 2 2 Stearic Acid — — — — — — — — — ZnSt 0.030.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 Talc 2.5 2.5 2.5 2.5 2.5 2.5 2.52.5 2.5 Polyamide 1 51 51 51 56 56 56 56 56 56 Polyamide 2 13 13 13 1414 14 14 14 14 Antioxidant 1 0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.320.32 Antioxidant 2 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13Antioxidant 3 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 PIBSA 10 1010 10 10 10 10 10 10 Compatibilizer — — — — — — — — — G′ at 1% strain,5878 5459 5744 7005 5750 3606 7293 7269 6841 100° C., kPa S′ at 200%strain, 5.8 5.1 6.4 5.5 5.1 7.6 5.1 5.3 5.3 215° C., dNm Barrel 7-11 260260 260 240 240 240 260 260 260 Temperature, ° C. 5a 5b 6 7 8a 8b 9 10BIMSM 1 100 100 100 100 100 100 100 100 ZnO 3 3 3 3 3 3 4 2 Stearic Acid— — 1 — — — — — ZnSt 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 Talc 2.52.5 2.5 2.5 2.5 2.5 2.5 2.5 Polyamide 1 56 56 56 56 56 56 56 21Polyamide 2 14 14 14 14 14 14 14 49 Antioxidant 1 0.32 0.32 0.32 0.320.32 0.32 0.32 0.32 Antioxidant 2 0.13 0.13 0.13 0.13 0.13 0.13 0.130.13 Antioxidant 3 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 PIBSA 10 1010 10 10 10 10 5 Compatibilizer — — — 1.5 — — — — G′ at 1% strain, 74656752 6623 6368 7600 7196 4801 6061 100° C., kPa S′ at 200% strain, 5.95.9 5.5 6.6 4.8 5.6 7.3 — 215° C., dNm Barrel 7-11 240 240 240 240 260260 240 240 Temperature, ° C.

Using the disclosed method of preparing the DVA, it is possible toobtain films having a permeability coefficient of not more than 0.16cc-mm/m^(g)-day-mmHg, or alternatively not more than 0.13cc-mm/m^(g)-day-mmHg, or in the range of 0.15 to 0.05 cc-mm/m²-day-mmHg;the lower values can be obtained by adjusting the formulation toelastomers and thermoplastic resins have independent lower permeabilitycoefficients and using the disclosed method of DVA preparation.

While the above specification and examples are specific to lowpermeability elastomers as the principal/primary elastomer, as thedescribed process is directed to a solution for creating DVAs of areactive mixture wherein interfacial grafting occurs, the process may beused with other types of elastomers and thermoplastics (and secondarymaterials) wherein the mixture is a reactive mixture (exclusive of anycross-linking reaction due to added curatives).

When numerical lower limits and numerical upper limits are listedherein, ranges from any lower limit to any upper limit are contemplated.While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be apparent to and can be readily made by thoseskilled in the art without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the scope of the claimsappended hereto be limited to the examples and descriptions set forthherein but rather that the claims be construed as encompassing all thefeatures of patentable novelty which reside in the present invention,including all features which would be treated as equivalents thereof bythose skilled in the art to which the invention pertains.

The invention has been described above with reference to numerousembodiments and specific examples. Many variations will suggestthemselves to those skilled in this art in light of the above detaileddescription. All such obvious variations are within the full intendedscope of the appended claims.

What is claimed is:
 1. A process for producing a dynamically vulcanizedalloy, the alloy comprising at least one elastomer and at least onethermoplastic resin, the process comprising the following consecutivesteps of: a) feeding the elastomer and a first portion of thethermoplastic resin into the initial feed throat of an extruder; b)mixing the elastomer and the first portion of thermoplastic resin; c)feeding a compatibilizer into the extruder; d) mixing the elastomer, thefirst portion of thermoplastic resin, and the compatibilizer to begingrafting of the elastomer with the thermoplastic resin without anysignificant curing of the elastomer; e) feeding a second portion of thethermoplastic resin into the extruder; and f) mixing the contents of theextruder under shear conditions to mix and cure the elastomer until theelastomer is dispersed as particles in a matrix of the thermoplasticresin and the elastomer particle achieve at least 80% cure forming adynamically vulcanized alloy; wherein the alloy has a G′ at 1% strainand 100° C. as determined according to ASTM D7605 of about 4,500 toabout 7,500 kPa.
 2. The process as claimed in claim 1, wherein saidelastomer is added directly into the feed throat without any priormixing with other components of the dynamically vulcanized alloy.
 3. Theprocess as claimed in claim 1, wherein at least one curative is fed intothe extruder with the second portion of the thermoplastic resin.
 4. Theprocess as claimed in claim 1, wherein after step e) and afterinitiation of cure of the elastomer particles, at least onecompatibilizer or viscosity modifier is fed into the extruder.
 5. Theprocess as claimed in claim 1, wherein during step a), c), or e) atleast one stabilizer is also fed into the extruder.
 6. The process asclaimed in claim 3, further comprising the step of pelletizing the atleast one curative with portions of the thermoplastic resin prior tofeeding the curative into the extruder, wherein the amount of thecurative added is about 2 to about 3 phr based on the alloy.
 7. Theprocess as claimed in claim 1, wherein the second portion ofthermoplastic resin added in step e) is 10 to 75 wt % of the totalthermoplastic resin in the alloy.
 8. The process as claimed in claim 1,wherein the second portion of thermoplastic resin is fed into theextruder at a location of 30% to 60% of an L/D ratio of the extruderwherein L is the screw length of the extruder and D is the maximum borewidth of the extruder barrel.
 9. The process as claimed in claim 1,further comprising the step of feeding a secondary elastomer into theinitial feed throat of the extruder.
 10. The process of claim 9, whereinthe secondary elastomer is maleic anhydride-modified copolymer.
 11. Theprocess as claimed in claim 1, wherein the thermoplastic resin isselected from the group consisting of polyamides, polyimides,polycarbonates, polyesters, polysulfonates, polyactones, polyacetals,acrylonitrile-butadiene-styrene resins, polyphenyleneoxide,polyphenylene sulfide, polystyrene, styrene-acrylonitrile resins,styrene maleic anhydride resins, aromatic polyketones, and mixturesthereof.
 12. The process as claimed in claim 1, wherein thethermoplastic resin is a polyamide selected from the group consisting ofnylon-6, nylon-12, nylon-6,6, nylon-6,9, nylon-6,10, nylon-6,12, nylon6,66 copolymer, nylon-11, and mixtures thereof.
 13. The process asclaimed in claim 1, wherein the elastomer is an isobutylene derivedelastomer.
 14. The process as claimed in claim 1, wherein the elastomeris a copolymer of an isobutylene and an alkystyrene.
 15. The process asclaimed in claim 1, wherein the elastomer is present in the alloy in anamount in the range of from about 2 to about 90 wt % based on the totalalloy blend weight or the thermoplastic resin is present in the alloy inan amount in the range of from 10 to 98 wt % based on the total alloyblend weight.
 16. The process as claimed in claim 1, wherein thethermoplastic resin is present in the alloy in an amount of 40 to 80phr.
 17. The process as claimed in claim 1, wherein the alloy has a S′at 200% strain and 215° C. as determined according to ASTM D7605 ofabout 4 to about 7 dNm.
 18. The process as claimed in claim 1, whereinthe extruder temperature is reduced by 5° to 50° C. after the secondportion of the thermoplastic resin is fed into the extruder.
 19. A filmformed from a dynamically vulcanized alloy manufactured by the processin accordance with claim
 1. 20. The film as claimed in claim 19, whereinthe film has a permeability coefficient of not more than 0.16cc-mm/m^(g)-day-mmHg.
 21. The film as claimed in claim 19, wherein thealloy has a G′ at 1% strain and 100° C. as determined according to ASTMD7605 of about 4,500 to about 7,500 kPa.